The ability to perform modern surgical procedures is facilitated in part by the development of instruments, sometimes referred to as tools, able to shape, remove or transform tissue. Electrosurgical tools are one such class of instruments. An electrosurgical tool system includes both a tool and a control console. The tool system includes at least two electrodes. The console sources a current between the electrodes. Some electrosurgical tools are monopolar tools. This type of tool includes a structural device designed for application to tissue that includes at least one electrode. This electrode is considered the active electrode. When this type of tool is employed, the system includes a ground pad. The ground pad is placed against the body of the patient to function as the return electrode. Other electrosurgical tools include structural devices designed for application to tissue that include at least two electrically disconnected electrodes. This type of tool is generally referred to as a bipolar tool. When a bipolar tool is in use, one or more electrodes function as the active electrode. The remaining one or more electrodes function as the return electrode.
When an electrosurgical tool is employed, current is flowed from the active electrode(s) through the target tissue to the return electrode(s). The internal resistance of the tissue converts the electrical energy to thermal energy that heats the tissue. The heating of the tissue causes the tissue to undergo a state change that is therapeutically advantageous. Some electrosurgical tools, such as forceps and loop pencils are used to cut or coagulate tissue to which they are applied. The coagulation stops blood loss from the tissue. Other electrosurgical tools are in the form of probes. Some probes are designed to ablate the tissue to which they are applied. One such class of probes ablates nerve cells that transmit chronic pain signals to the brain. Other electrosurgical tools remove relatively large sections of tissue to accomplish other therapeutic effects.
An electrosurgical tool system includes more than the tool. The system also includes a control console and a cable. The console includes a power signal generator. The power signal generator outputs an AC power signal at a potential often above 100 Volts to the electrosurgical tool. A control module integral with the console regulates the power signal generator to allow characteristics of the power signal applied to the tool to be varied. Tool power signal characteristics that can be varied include: voltage; current; signal frequency; pulse duty cycle; pulse envelop; and pulse repetition frequency. The characteristics of the power signal applied to a tool vary with tool type, the type of procedure and preferences of the individual practitioner.
The cable includes conductors over which the power signal is applied to the tool.
Often, an electrosurgical tool and its complementary control console are provided as a single system. This is because a particular tool is typically designed to receive power signals that have a specific set of characteristics. It is common practice to design the console so the console can only source power signals that can be applied to the tool with which the console is to be used. The practitioner is able to vary characteristics of the power signal within a specific range appropriate for that tool. A disadvantage of these systems is that should a medical facility use plural different tools with very different power requirements, the facility is obligated to provide plural control consoles that differ only in the characteristics of the power signals they source.
A remedy to this arrangement is to provide a control console able to source energization signals over a wide range of output characteristics. Such a system could rely on the operator to manually set the characteristics of the sourced power signal. If an individual is allowed to so set the characteristics of the power signal, the console could inadvertently be configured to source a power signal that is inappropriate for the tool to which the signal is applied. Such configuration of the system could result in the console sourcing a power signal that causes the tool to malfunction. A more serious result of such misconfiguration is that the system applies a current to the patient that inadvertently causes tissue damage.
A solution to the above problem is to provide a NOVRAM in the surgical tool and a complementary assembly in the console to read the tool NOVRAM. The NOVRAM, a non-volatile memory, stores data that describe the characteristics of the power signal that should be sourced to the tool. The console processing circuit reads these data. Based on these data, the processing circuit ensures that the power supply components internal to the console only source power to the tool that have appropriate characteristics for the tool. The Applicants' Assignee's U.S. Pat. No. 6,017,354 and its Application U.S. Pub. No US 2007/0016185 A1, both of which are incorporated herein by reference, disclose how it is possible to provide an electrosurgical tool system with such components.
Configuring an electrosurgical tool system automatically based on data in a memory integral with the tool facilitates rapid system set-up. Limiting the extent to which a tool power signal can be adjusted based on the data in the tool memory reduces the likelihood human error can result in an incorrect system set-up. Nevertheless, there are some limitations with known systems. This type of system requires a cable with conductors to supply power to the tool electrode/electrodes and additional conductors over which signals are read from the tool memory. The need to provide the cable with these multiple conductors makes it more expensive to provide than a conventional two-wire, power signal only, cable. Requiring use of such a cable makes it difficult to use the control console with tools not equipped with internal memories. A medical facility would like a console to have this utility so the console is also able to energize different types of tools, even tools without memories. However, if the console is configured to power both types of tools, different cables would be required. A first cable is required for tools that have memories. A second cable is required for tools without memories. This requires the facility to keep both types of cables available for use. Further, when configuring the system, personnel must take the time to ensure that the attached cable is appropriate for the tool being used.
The above-described tool with memory assembly is itself of limited utility. This is because, as described above, use of the tool requires use of the special cable with at least one conductor solely for sourcing power and at least one conductor solely for facilitating the reading of the data from the tool memory. This type of cable could not therefore be connected to a conventional console that source power to conventional, memoryless, tools. Accordingly, if one were to provide the above-described tool, use of the tool would be limited to the consoles specifically designed to receive the cable designed for use with this tool.
Also, there are procedures when it is desirable to, with the same tool, power signals having different characteristics to the same section of tissue. Specifically there are times when it is desirable to first cut tissue and then coagulate the cut tissue. The signal used to cut tissue is typically in the form of a continuous AC waveform. The electrical energy contained in the tissue quickly vaporizes the water internal to the cells of the tissue so that the cells burst. The cell bursting is the cutting of the tissue.
As soon as the tissue is cut, it is often desirable to apply a second signal to coagulate the tissue; stop the blood loss. A coagulation signal may have the same maximum peak-to-peak voltage as a cut signal. However, the coagulation signal is typically not applied as a continuous signal. Instead when the system is in the coagulation mode, the signal applied to the tool is typically in an on-off-on-off pulse form. Each pulse may consist of a number of cycles of the AC power signal. Sometimes each cycle of a pulse has the same peak-to-peak voltage. Sometimes the initial cycle/cycles of a signal pulse have a first, relatively high peak-to-peak voltage; the remaining cycles have peak to peak voltages that decay from the peak-to-peak voltage of the initial cycle/cycles. The coagulation power signal is not a continuous power signal to limit the current flowed through the tissue. The limiting of tissue current flow reduces the extent to which the current flow heats the tissue. Consequently, instead of the current generating heat that causes cell destruction, only enough heat is generated to cause fluid, blood, coagulation.
Stated another way, the crest factor, the ratio of peak voltage to the rms voltage, for a coagulation power signal is typically greater than the crest factor for a cut power signal.
It is a relatively simple task to provide a monopolar surgical tool with on tool switches that allow the practitioner to select which type of power signal is sourced to the tool. However, to date, it has proved difficult to provide a bipolar tool with the same type of on-tool control. When a practitioner wants to use such a tool to sequentially apply different currents to a tissue, means other than an on-tool switch are used to set the current type. Sometimes, for example, a practitioner must rely on another individual to manually actuate a control member integral with the console. Each time the practitioner wants to switch current states for the tool he/she must: give a verbal command; wait for the assistant to hear the command; wait for the assistant to actuate the appropriate switch; and then wait for the assistant to inform the practitioner the command was acted upon. Having to take all these steps, can appreciably increase the time it takes for the tool current settings to be switched. Given the length of these time gaps, some practitioners find bipolar electrosurgical tools unsuitable for performing procedures for which such tools are otherwise well designed.
Further, there are times when a practitioner wants to provide irrigation fluid when using an electrosurgical tool. Both monopolar and bipolar electrosurgical tools that include conduits through which irrigation fluid is pumped to the site the tool is applied are known. However, to date, it has proved difficult to provide a tool, especially a bipolar tool that allows the practitioner to, with one hand, both position the tool at the site and control both tool activation and whether or not irrigation fluid is discharged at the site.